The present embodiments relate to emission tomography. In emission tomography, an added radioisotope in a patient gathers at locations of metabolic function. The added radioisotope causes emissions. The emission tomography system detects the emissions. Various approaches for detecting emissions may be used, such as Single Photon Computed Tomography (SPECT) or Positron Emission Tomography (PET). The detected emissions are reconstructed from a space defined by the detector to an image or object space representing the activity distribution relative to the patient.
The activity concentration or counts may be underestimated due to the partial volume effect. The measured activity as reconstructed is less than the actual activity for small volumes with linear dimensions less than roughly 3 times the full width half maximum (FWHM) of the effective point spread function (PSF) of the detector (i.e., the emission tomography imaging system). Discretization may also cause edge voxels to involve a mix of different tissues. Due to the partial volume effect, the reconstructed activity concentration near edges of organs or other objects may be lower than the actual activity concentration.
The partial volume effect may be corrected, in part, by incorporation of the PSF into the system matrix used for forward and back-projection, but this correction may be limited. The partial volume effect may be corrected using anatomical information. The tissue is divided into regions of uniform function, which assumes little variation in the same type of tissue. Voxels in different regions are then corrected, but this approach requires segmentation of different tissues. The correction occurs post reconstruction by scaling of activity in a volume. The scaling factor is known from calibration measurements. Voxel based approach also use anatomy. These approaches are generic.